Since strengthened glass used for displays of portable information equipment and the like is weak against scratches, a surface of the strengthened glass is coated with an antifouling film. However, adhesion between the strengthened glass and the antifouling film is poor. Therefore, in order to improve the adhesion between the antifouling film and the strengthened glass, a base film such as a SiO2 film or the like is formed on the strengthened glass, and the antifouling film is formed on the base film. The SiO2 film can be formed on the strengthened glass by using, for example, a plasma CVD (Chemical Vapor Deposition) device which makes use of ICP (Inductively Coupled Plasma) or the like.